Baxter is not full Yorkie, and has always had floppy ears. He's five months now and they are just as floppy as ever. I never shaved the hair around them, because I think he looks SO cute with his hairy, floppy ears!
But I've heard that if they are teething, there ears may go up and down... three months sound young, so if you give it time, they may stand up on their own.